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the study of the effects of ionizing radiation on living tissue
radiation biology
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T or F. in diagnostic radiography, not all x-rays pass through the patient and reach the dental x-ray film; some are absorbed by patient tissues
true
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the total transfer of energy from the x ray photon to the pt tissues
absorption
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what happens when x-ray energy is absorbed by pt tissues?
chemical changes occur that result in biologic damage
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What are 2 specific mechanisms of radiation injury?
- ionization
- free radical formation
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x-rays are a form of________ radiation, when x rays strike patients tissues,_______results
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what is produced throught he photoelectric effect, or compton scatter, and results in the formation of a positive atom and a dislodged negative electron?
ionization
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forms a positive atom and a dislodged negative electron
ionization
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Ionization caus____ ______in the cell that results in biological damage
chemical changes
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Ionization causes chemical changes in the cell that results in ____ _______
biological damage
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X radiation causes cell damage primarily through formation in which type of radiation injury?
free radical formation
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occurs when an x ray photon ionizes water
free radical formation
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What is the primary component of living cells?
water
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Ionization of water results in the production of_____ and____ _____ ____
- hydrogen
- hydroxyl free radicals
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an uncharged (neutral) atom or molecule that exists with a single, unpaired electron in its outermost shell
free radical
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true or false. a free radical is highly reactive and unstable
true
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What are 3 ways that free radicals can achieve stability?
- recombine without changes in the molecule
- combine with ordinary molecules and form a toxin (hydrogen peroxide) capable of producing widespread cellular changes
- combine with other free radicals and cause change
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What toxin s formed when a free radical combines with ordinary molecules and forms a toxin?
hydrogen peroxide
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Damage to living tissues due to exposure to ionizing radiation may result from what 2 things?
- direct hit and absorption of an x-ray photon within a cell
- absorption of an x-ray photon by water within a cell accompanied by free radical formation
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What are the 2 theories about how radiation damages bioligic tissues?
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suggests that cell damage results when ionizing radiation directly hits critical areas whtin the cell
direct theory
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What is an example of a critical area in the cell in the direct theory?
DNA
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Do direct injuries from exposure toionizing radiation occur frequently or infrequently?
infrequently, most x ray photons pass through the cell and cause little or no damage
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suggests the x-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell
indirect theory
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when x-ray photons are absorbed by water within a cell ___ ____ _______ results
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In the indirect theory the free radicals combine to form_____ which cause cellular dysfunction and_______ _______
- toxins (H2O2)
- biologic damage
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an indirect injury results because the _____ ______ combine and form ______
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Why is the chance of free radical formation and indirect injury treat?
because cells are composed of 70-80% water
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used to correlate the 'response' or damage, of tissues with the 'dose' or amount, of radiation recieved
dose-response curve
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When dose and damage are plotted on a graph, a______, ________ relationship is seen
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indicates tat the response of the tissues is directly proportional to the dose
linear
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indicates that a threshold dose level for damage does not exist, suggests that no matter how small the amount of radiation recieved, some damage occurs
nonthreshold
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Is there a safe amount of radiation exposure?
NO!
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Biologic effects from radiation can be classified as what 2 types?
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______ effects occur as a direct function of dose
stochastic
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In what effect does the probability of occurrence increase with increasing absorbed dose; however, the severity of effects does not depend on the magnitude of the absorbed dose?
stochastic effect
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true or false. stochastic effects do not have a dose threshold
true
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What are 2 examples of stochastic effects?
- cancer (tumor) induction
- genetic mutations
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What is another name for nonstochastic effects?
deterministic effects
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somatic effects that have a threshold and increase in severity with increasing absorbed dose
nonstochastic (deterministic) effects
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What are 4 examples of nonstochastic effects?
- erythema
- loss of hair
- cataract formation
- decreased fertility
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Which biologic effect requires more radiation doses to seriously impair health?
nonstochastic
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chemical reactions (ionization, free radical formation) that follow the absorption of radiation occur rapidly at the______ _______
molecular level
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varying amounts of time are required for chemical reaction (ionization, free radical formation) changes to alter____ and _____ _______
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true or false. the observable effects of radiation are not visible immediately after exposure
true
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the time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs
latent period
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The latent period may be short or long depending on what 2 things?
- total dose of radiation recieved
- amount of time, or rate it took to recieve the dose
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The more radiation recieved, and the faster the dose rate, the_________the latent period
shorter
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cell death, changes in cell function, breaking or clumping of chromosomes, formation of giant cells, cessateion of mitotic activity, or abnormal mitotic activity are all examples of what?
period of injury
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What is the last event in the sequence of radiation injury?
recovery period
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What is the order of the radiatio injury sequence?
latent period - period of injury - recovery period
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true or false. all cellular radiation injuries are permanent
FALSE!!!
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with each radiation exposure, cellulear damage is followed by____
repair
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Most of the damage caused by _______ radiation is repaired with cells of the body.
low-level
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effects of radiaion exposure are additive and damage that remains unrepaired accumulates in the tissues, is termed:
cumulateive effects
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____________ of repeated radiation exposure can lead to health problems.
cumulative effects
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Radiation effect on hematopoietic (blood forming):
leukemia
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radiation effects on reprocuctive (ova, sperm)
mutations
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radiation effects on thyroid
carcinoma
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radiation effects on skin
carcinoma
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radiation effects on eyes
cataracts
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Name 5 factors that influence radiation injury:
- total dose
- dose rate
- amount of tissue irradiated
- cell sensitivity
- age
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the quantity of radiation received, or the total amount of radiation energy absorbed
total dose
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the rate at which exposure to radiation occurs and absorption takes place
dose rate
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dose rate = _______
dose/time
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Why does more radiation damage take place with high dose rates?
because a rapid delivery o radiation does not allow time for the cellular damage to be repaired
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the areoas of the body exposed to radiation
amount of tissue irradiated
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What is an example of total body irradiation?
a person exposed to a nuclear energy disaster
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extensive radiation injury occurs when large areas of the body are exposed because of the damage that occurs to the______ _________ _________
blood forming tissues
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true or false. cell sensitivity affects radiation injury
true
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are children or adults more susceptible to radiation damage?
children
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